1. Field of the Invention
The present invention relates generally to communication devices, semiconductor integrated circuit devices, and communication systems, and more particularly to a communication device, a semiconductor integrated circuit device, and a communication system for performing bidirectional serial communication by using a clock line and a data line.
2. Description of the Related Art
In recent years and continuing, battery packs of portable personal computers or digital cameras are provided with fuel gauges for measuring the residual battery energy quantity. A fuel gauge IC is an IC chip that calculates the residual battery energy quantity by integrating the charge and discharge currents of the battery, and reports the calculated residual battery energy quantity to a main unit circuit of a main unit of the portable personal computer or the digital camera (Patent Document 1).
The fuel gauge IC itself consumes power. Thus, in order to make the battery last longer, a low-power consuming fuel gauge IC is desired. Communication with the fuel gauge IC is performed with an I2C (Inter-Integrated Circuit, I square C) communication method. An I2C controller is installed in the fuel gauge, and the I2C controller communicates with the main unit circuit.
FIG. 8 illustrates an example of an operation performed in the conventional I2C communication method. Operation timings of data signals SDA are illustrated in (A), and operation timings of clock signals SCL are illustrated in (B).
In response to detecting starting conditions (for starting communication) at a time t1, the I2C controller sequentially outputs clock signals SCL at substantially fixed intervals as shown in (B). Based on the clock signals SCL shown in (B), data signals SDA are communicated between another device as shown in (A).
If the I2C controller comes to a standby status, it takes time for the I2C controller to wake up from the standby status. Accordingly, it takes time to start communications and responses to another device are thus delayed, such that communications with another device cannot be properly performed. To prevent such a circumstance, the I2C controller is constantly operated to be constantly ready for returning responses to another device.
Patent Document 1: Japanese Laid-Open Patent Application No. 2001-174534
In this type of conventional communication system, the communication controller (e.g., I2C controller) is constantly operated to be ready for immediately responding to another device when starting conditions are satisfied. Thus, power consumption of the communication controller cannot be reduced.